Oxygen self-diffusion in cerium oxide doped with Nd
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Manabu Komatsu and Hajime Haneda National Institute for Research in Inorganic Materials, 1-1 Namiki Tsukuba, Ibaraki 305-0044, Japan
Soichiro Sameshima and Yoshihiro Hirata Kagoshima University, 1-21-40 Korimoto Kagoshima, Kagoshima 890-0065, Japan (Received 7 March 2000; accepted 29 September 2000)
Polycrystalline Ce0.77Nd0.23O1.885 having a relative density in excess of 98% was prepared. Oxygen diffusion experiments were performed for the temperature range from 750 to 1100 °C, in an oxygen partial pressure of 6.6 kPa. The concentration profile of 18O in the specimens following diffusion annealing was measured by secondary ion mass spectroscopy (SIMS). The oxygen self-diffusion coefficient obtained using secondary ion mass spectrometry was expressed by D ⳱ 6.31 × 10−9 exp(−53 kJ mol−1/RT) m2 s−1 and was in the extrinsic region. The oxygen diffusion coefficient of Ce0.77Nd0.23O1.885 was larger than that of Ce0.8Y0.2O1.90; it was close to those of Ce0.6Y0.4O1.80 and Ce0.69Gd0.31O2−␦. The oxygen diffusion coefficient obtained by the tracer method at 700 °C agreed with that calculated from the electrical conductivity in Ce0.77Nd0.23O1.885. The activation energy of the surface exchange coefficient was 94 kJ mol−1, and the values of the surface exchange coefficient were similar to those of stoichiometric CeO2 and ThO2.
I. INTRODUCTION
CeO2 has recently attracted attention because of its high electrical conductivity at low temperatures. However, CeO2 exhibits both electronic and ionic conductivity. One way to reduce the electronic conductivity is to dope the oxide with several rare earth oxides. Doping CeO2 with trivalent impurities creates defects that change the diffusion behavior of the oxide. Thus, CeO2 doped with rare earth elements is of interest. Several rare earth oxides exhibit high solubility to cerium oxide. Recently, several researchers1–12 have investigated electrical conductivity, oxygen diffusion coefficient, and nonstoichiometry in Gd–CeO2. Schneider et al.2 reported that Gd–CeO2 exhibited higher electrical conductivity than undoped CeO2. The solubility of neodium oxide (Nd2O3) into CeO2 is larger than gadolinium oxide (Gd2O3). Consequently, the electrical conductivity behavior of CeO2 doped with Nd is of interest. Electrical conductivity in CeO2 doped with Nd has been measured by Dirstine et al.,6 but the oxygen diffusion coefficient has not been measured. Since the ionic conductivity is closely related to the oxygen self-diffusion coefficient, to understand the conductivity behavior of the oxide both the oxygen diffusion coefficient and the electrical conductivity of the material should be measured. The purpose of the present study was, therefore, to measure the oxygen diffusion coefficient in CeO2 doped with Nd using secondary ion mass spectroscopy (SIMS). J. Mater. Res., Vol. 16, No. 1, Jan 2001
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In addition, the oxygen diffusion coefficients calculated from the electrical conductivity of CeO2 doped with rare earth elements (Nd, Y, Gd) was co
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